This invention relates to antennas, phased array antennas, and specifically to a one-dimensional electromagnetic band gap (EBG) waveguide phase shifter based electronically scanned array (ESA) horn antenna.
Phased array antennas offer significant system level performance enhancements for advanced communications, data link, radar, and SATCOM systems. The ability to rapidly scan the radiation pattern of the array allows the realization of multi-mode operation, LPI/LPD (low probability of intercept and detection), and A/J (antijam) capablities. One of the major challenges in phased array design is to provide a cost effective and environmentally robust interconnect and construction scheme for the phased array assembly. Additional requirements include phased array antenna phase shifting methods and techniques.
It is well known within the art that the operation of a phased array is approximated to the first order as the product of the array factor and the radiation element pattern as shown in Equation 1 for a linear array.
                                                                        E                A                            ⁡                              (                θ                )                                      ≡                                     ⁢                                            E              p                        ⁡                          (                              θ                ,                ϕ                            )                                            ︸                          Radiation              ⁢                                                          ⁢              Element              ⁢                                                          ⁢              Pattern                                      ⁢                                  ⁢                                            [                                                exp                  ⁡                                      (                                                                  -                        j                                            ⁢                                                                                          ⁢                                                                        2                          ⁢                                                                                                          ⁢                          π                          ⁢                                                                                                          ⁢                                                      r                            o                                                                          λ                                                              )                                                                    r                  o                                            ]                                      ︸                              Isotropic                ⁢                                                                  ⁢                Element                ⁢                                                                  ⁢                Pattern                                              ·                                                    ∑                N                            ⁢                                                A                  n                                ⁢                                  exp                  ⁡                                      [                                                                  -                        j                                            ⁢                                                                                          ⁢                                                                        2                          ⁢                          π                                                λ                                            ⁢                      n                      ⁢                                                                                          ⁢                      Δ                      ⁢                                                                                          ⁢                                              x                        ⁡                                                  (                                                                                    sin                              ⁢                                                                                                                          ⁢                              θ                                                        -                                                          sin                              ⁢                                                                                                                          ⁢                                                              θ                                o                                                                                                              )                                                                                      ]                                                                                      ︸                              Array                ⁢                                                                  ⁢                Factor                                                                        Equation        ⁢                                                  ⁢                                                ⁢        1            
Standard spherical coordinates are used in Equation 1 and θ is the scan angle referenced to bore sight of the array. Introducing phase shift at all radiating elements within the array changes the argument of the array factor exponential term in Equation 1, which in turns steers the main beam from its nominal position. Phase shifters are RF devices or circuits that provide the required variation in electrical phase. Array element spacing is related to the operating wavelength and sets the scan performance of the array. All radiating element patterns are assumed to be identical for the ideal case where mutual coupling between elements does not exist. The array factor describes the performance of an array of isotropic radiators arranged in a prescribed grid for a two-dimensional rectangular array grid.
Co-pending application Ser. No. 10/273,459 effectively resolves the phased array interconnect problem by utilizing fine pitch, high-density circuitry in a thin self-shielding multi-layer printed wiring assembly. The new approach utilizes the thickness dimension of an array aperture wall (parallel to bore sight axis) to provide the surface area and volume required to implement all of the conductive traces for phase shifter bias, ground, and control lines.
A packaging, interconnect, and construction approach is disclosed in co-pending application Ser. No. 10/273,872 that creates a cost-effective EMXT (electromagnetic crystal)-based phased array antennas having multiple active radiating elements in an X-by-Y configuration. EMXT devices are also known in the art as tunable photonic band gap (PBG) and tunable electromagnetic band gap (EBG) substrates.
A detailed description of a waveguide section with tunable EBG phase shifter technologies is available in a paper by J. A. Higgins et al. “Characteristics of Ka Band Waveguide using Electromagnetic Crystal Sidewalls” 2002 IEEE MTT-S International Microwave Symposium, Seattle, Wash., June 2002. Each element is comprised of EMXT sidewalls and a conductive (metallic) floor and ceiling. Each EMXT device requires a bias voltage plus a ground connection in order to control the phase shift for each element of the antenna by modulating the sidewall impedance of the waveguide. By controlling phase shift performance of the elements, the beam of the antenna can be formed and steered.
One-dimensional electronic beam steering is adequate for many communication and radar systems, with mechanical steering providing adequate beam steering rates on the second dimension, if required. Specific bands of current interest include C- and X-band for SATCOM and meteorological, multimode, and fire control radars, Ku-band (10-12 GHz), Ka-band (20/30 GHz), and Q-band (44 GHz) for satellite communication (SATCOM) systems and 38 GHz for FCS Future Combat Systems (FCS) communications and radar. For example, the FCS ground-to-ground radar/communication function requires only rapid beam scanning in azimuth with a static fan beam in elevation. Another example is an elevation only ESA for commercial multimode weather radar. Additional examples include ground-based SATCOM on-the-move and non-fighter airborne SATCOM that do not require rapid beam agility in two dimensions.
Frequently the above-mentioned systems have extremely aggressive recurring cost requirements. One-dimensional beam scanning significantly reduces the ESA phase shifter count and beam steering computer/interconnect complexity, all which directly contribute to cost. To illustrate this complexity issue, consider the following: to a first order, a N×N, two-dimensional ESA requires N2 phase shifters, each with commensurate beam steering control and interconnect requirements, where as a one-dimensional ESA of the same electrical size only requires N phase shifters, control and interconnect. For N=200, the two-dimensional ESA would require 40,000 phase shifters where as the one-dimensional ESA of the same size would require 200 phase shifters.
A need exists for a cost-effective, low-loss, robust, one-dimensional electronically scanned phased arrays with extremely fast beam steering rates.